1. Field of the Invention
The present invention relates to an optical position detection device employing a semiconductor position detection element and to a distance measurement device wherein object distance is measured by using an optical position detection device to detect the reflected light of a spot beam or slit beam illuminating this object.
2. Related Background Art
In a semiconductor position detection element, incident light is subjected to photoelectric conversion to generate a photoelectric current (carriers) and, dependent on the position of incidence of the beam, a first signal current I1 is output from a first output terminal and a second signal current I2 is output from a second output terminal. The sum (I1+I2) of the first signal current and second signal current depends on the incident light beam intensity. If the sum (I1+I2) of the first signal current and second signal current is fixed, the difference (I1xe2x88x92I2) of the first signal current and second signal current corresponds to the position of incidence of the beam. An optical position detection device detects the position of beam incidence using such a semiconductor position detection element. Also, a distance measurement device comprises a light-emitting unit in addition to this optical position detection device and the distance to the object is detected by photodetection by the semiconductor position detection element in the optical position detection device of the reflected light of a spot beam illuminating the object by the light-emitting unit.
In a conventional optical position detection device the ratio (V1/V2) of a first signal voltage V1 derived from the first signal current I1 output from the semiconductor position detection element and a second signal voltage V2 derived from the second signal current I2, is found and is used as an output indicating the position of beam incidence. Alternatively, in a conventional optical position detection device, the sum of the first signal voltage V1 and the second signal voltage V2 (V1+V2) and the difference (V1xe2x88x92V2) are found, the difference is divided by the sum, and the result of this division ((V1xe2x88x92V2)/(V1+V2)) is used as an output indicating the position of beam incidence (see for example Laid-open Japanese Patent Publication No. H.2-247504). Thus, in a conventional optical position detection device, in whichever case, division means were considered to be necessary for obtaining an output indicating the position of beam incidence on the semiconductor position detection element. In addition, the foregoing publication discloses a technique for improving resolution of the position of beam incidence wherein the signal voltages that are respectively to constitute the divisor and dividend are multiplied by a suitable multiplication factor before being subjected to A/D conversion, after which division is performed in order to output the result of this division as a digital value in a suitable range.
The division means in a conventional optical position detection device as described above may be realized by either analogue circuitry or digital circuitry but hardware costs are high owing to the difficulty of miniaturization due to the size of this circuitry, or the time required for division processing is long due to the large amount of calculation. Also, miniaturization of the division means disclosed in the above publication is difficult and hardware costs are high owing to the need to provide a large number of amplification circuits and A/D conversion circuits.
Furthermore, if a plurality of semiconductor position detection elements are provided, if only a single set of the processing circuits (including the current/voltage conversion circuit, division circuit, amplification circuit and A/D conversion circuit etc) that find the position of beam incidence from the signal current output from the semiconductor position detection elements is provided, the time required for finding the position of beam incidence is further lengthened. On the other hand, if the same number of the aforesaid processing circuits are provided as the number of semiconductor position detection elements, the size of the circuitry is further increased and hardware costs are further raised.
Conventional distance measurement devices including such optical position detection devices are likewise subject to the problems of large circuit size and long processing time.
The present invention was made in order to solve the problems mentioned above, its object being to provide an optical position detection device wherein the size of the circuitry is small, processing time short, and excellent resolution of the position of beam incidence output as a digital signal is obtained and a distance measurement device employing such an optical position detection device. A first optical position detecting device according to the present invention comprises: (1) a semiconductor position detection element whereby an incident beam is subjected to photoelectric conversion, and that outputs a first signal current from a first output terminal and outputs a second signal current from a second output terminal in response to the position of incidence of this beam; (2) a first current/voltage conversion unit that inputs the first signal current that is output from the first output terminal of the semiconductor position detecting element and outputs a first signal voltage in accordance with this first signal current; (3) a second current/voltage conversion unit that inputs the second signal current that is output from the second output terminal of the semiconductor position detecting element and outputs a second signal voltage in accordance with this second signal current; (4) a selection circuit that compares the magnitude of the respective values of the first signal voltage output from the first current/voltage conversion unit and the second signal voltage output from the second current/voltage conversion unit and that outputs a comparison signal indicating the result of this comparison and, of the first and the second signal voltages, respectively selects and outputs a maximum signal (maximum signal voltage) whose voltage is the larger and a minimum signal (minimum signal voltage) whose voltage is the smaller; (5) an A/D conversion circuit wherein an A/D conversion range is set in accordance with the maximum signal output from the selection circuit and that converts the minimum signal output from the selection circuit into a digital signal and outputs this digital value; and (6) an incidence position calculating unit that finds the incidence position of the beam on the semiconductor position detecting element, using the comparison signal output from the selection circuit and the digital output which is output from the A/D conversion circuit.
With the first optical position detection device according to the present invention, when a beam of light is incident on the semiconductor position detection element, this beam is subjected to photoelectric conversion and, depending on the position of incidence of this beam, a first signal current I1 is output from the first output terminal and a second signal current I2 is output from the second output terminal. The first signal current I1 is input to the first current/voltage conversion unit so that a first signal voltage V1 is output based on this first signal current I1. In the same way, the second signal current I2 is input to the second current/voltage conversion unit so that a second signal voltage V2 is output based on this second signal current I2. The first and second signal voltages V1 and V2 are respectively input to the selection circuit where the magnitudes of their respective values are compared and a comparison signal indicating the comparison result is output and, of the first and second of signal voltages V1 and V2, that of larger voltage is designated as maximum signal Vmax and that of smaller voltage is designated as the minimum signal Vmin, these being respectively selected and output. In the A/D conversion circuit, an A/D conversion range is then set in accordance with the maximum signal Vmax which is output from the selection circuit. Suitably, by setting the A/D conversion range equal to the maximum signal Vmax voltage, the entire A/D conversion range can be effectively utilized. Also, the A/D conversion circuit converts the voltage of the minimum signal Vmin that is output from the selection circuit to a digital signal and outputs its digital value. This digital value indicates the ratio (Vmin/Vmax). The position of beam incidence on the semiconductor position detection element is found by the incidence position calculating unit from the comparison signal that is output from the selection circuit and the digital output that is output from the A/D conversion circuit. Division processing can therefore be implemented substantially concurrently with the A/D conversion in the A/D conversion circuit, making it possible to reduce the circuit size, lowering hardware costs, and to shorten processing time.
Also, a first optical position detection device according to the present invention further comprises a limit detecting unit that monitors the voltage of the maximum signal output from the selection circuit and that outputs a signal indicating the fact, if this voltage is smaller than the threshold value. In this case, the voltage of the maximum signal that is output from the selection circuit is monitored by the limit detecting unit and a signal indicating this fact is output if this voltage is smaller than the threshold value. Spurious detection can therefore been prevented by making a judgment as to whether or not the beam that is to be detected is incident in the photosensitive region of the semiconductor position detection element.
Also, a first optical position detection device according to the present invention may further comprise a plurality of sets of the semiconductor position detecting element, the first current/voltage conversion unit, the second current/voltage conversion unit and the selection circuit wherein the A/D conversion circuit inputs sequentially the maximum signal (maximum signal voltage) and the minimum signal (minimum signal voltage) output from the selection circuits of each set and the incidence position calculating unit sequentially inputs the comparison results (comparison signals) output from the selection circuits of each set. Furthermore, the limit detection unit may sequentially input the maximum signal output from the selection circuit of each set. If a plurality of semiconductor position detection elements are arranged in the form of an array, the position of beam incidence on a two dimensional photosensitive region can be detected. Also, even if the semiconductor optical detection element is constructed in multi-channel form by providing individual first and second current/voltage conversion units and selection circuits for each semiconductor position detection element but providing the A/D conversion circuit, incidence position calculating unit and limit detecting unit in common for each of the semiconductor position detecting elements, circuit size can be reduced and processing time shortened. It should be noted that the maximum signal and minimum signal are found for each set.
A second optical position detecting device according to the present invention comprises: (1) a semiconductor position detection element whereby an incident beam is subjected to photoelectric conversion, and that outputs a first signal current from a first output terminal and outputs a second signal current from a second output terminal in response to the position of incidence of this beam; (2) a first current/voltage conversion unit that inputs the first signal current that is output from the first output terminal of the semiconductor position detecting element and outputs a first signal voltage in accordance with this first signal current; (3) a second current/voltage conversion unit that inputs the second signal current that is output from the second output terminal of the semiconductor position detecting element and outputs a second signal voltage in accordance with this second signal current; (4) an addition circuit that adds the first signal voltage output from the first current/voltage conversion unit and the second signal voltage output from the second current/voltage conversion unit and outputs a sum signal (third signal voltage) indicating the sum obtained by this addition; (5) a selection circuit that selects and outputs the first signal voltage output from the first current/voltage conversion unit or the second signal voltage output from the second current/voltage conversion unit; and (6) an A/D conversion circuit wherein an A/D conversion range is set in accordance with the sum signal output from the addition circuit and that converts the first or the second signal voltage selected and output by the selection circuit into a digital signal, and outputs its digital value.
With the second optical position detection device according to the present invention, when a beam of light is incident on the semiconductor position detection element, this beam is subjected to photoelectric conversion and, depending on the position of incidence of this beam, a first signal current I1 is output from the first output terminal and a second signal current I2 is output from the second output terminal. The first signal current I1 is input to the first current/voltage conversion unit so that a first signal voltage V1 is output based on this first signal current I1. In the same way, the second signal current I2 is input to the second current/voltage conversion unit so that a second signal voltage V2 is output based on this second signal current I2. The first and second signal voltages V1 and V2 are respectively added by the addition circuit to output a sum signal Vsum=V1+V2 indicating the sum obtained by this addition. Also, the first or second signal voltage V1 or V2 is selected and output by the selection circuit. In the A/D conversion circuit, an A/D conversion range is set in accordance with the sum signal Vsum output from the addition circuit. Suitably, by setting the A/D conversion range equal to the sum signal Vsum voltage, the entire A/D conversion range can be effectively utilized. Also, the A/D conversion circuit converts the first or second signal voltage V1 or V2 selected and output by the selection circuit to a digital signal whose digital value is output. This digital output indicates the ratio (V1/Vsum) or the ratio (V2/Vsum). Consequently, division calculation can be implemented substantially concurrently with A/D conversion by the A/D conversion circuit, so circuit size can be reduced, lowering hardware cost, and processing time shortened. It should be noted that the position of incidence of the beam on the semiconductor position detecting element can be found using the digital value indicating the ratio ((V1xe2x88x92V2)/Vsum); in this case, suitably an incidence position calculating unit is provided wherein the selection circuit sequentially selects the first and second signal voltages V1 and V2, and the A/D conversion circuit sequentially outputs digital signals indicating respectively the ratio (V1/Vsum) and the ratio (V2/Vsum), and, by inputting these digital signals, the ratio of these two is calculated and output.
Also, a second optical position detection device according to the present invention may further comprise a limit detecting unit that monitors the value of the sum signal output from the addition circuit and that outputs a signal indicating the fact, if this value is smaller than the threshold value. In this case, as the value of the sum signal that is output from the addition circuit is monitored by the limit detecting unit, a signal indicating this fact is output if this value is smaller than the threshold value. Spurious detection can therefore been prevented by making a judgment as to whether or not the beam that is to be detected is incident in the photosensitive region of the semiconductor position detection element.
Also a second optical position detection device according to the present invention may comprise a plurality of sets of the semiconductor position detecting element, the first current/voltage conversion unit, the second current/voltage conversion unit, the addition circuit and the selection circuit wherein the A/D conversion circuit inputs sequentially the sum signal output from the addition circuits and the first or the second signal voltage selected and output by the selection circuits of each set. Furthermore, the limit detecting unit may sequentially input the sum signals that are output from the addition circuits of each set. If the plurality of semiconductor position detecting elements are arranged in the form of an array, the position of incidence of the beam in a two dimensional photosensitive region can be detected. Also, even if the semiconductor optical detection element is constructed in multi-channel form by providing individual first and second current/voltage conversion units and addition circuits for each semiconductor position detection element but providing the A/D conversion circuit, incidence position calculating unit and limit detecting unit in common for each of the semiconductor position detecting elements, circuit size can be reduced and processing time shortened. It should be noted that the maximum signal and minimum signal are found for each set.
A first or second optical position detection device according to the present invention used with a light-emitting unit that illuminates the object with a spot beam or slit beam (1) the first current/voltage conversion unit may include: (1a) a first integrating circuit that integrates charge in accordance with the first signal current and outputs a signal voltage corresponding to the amount of this integrated charge; and (1b) a first difference calculating circuit that finds the difference of the signal voltage output from the first integrating circuit when no light from the light-emitting unit illuminates the object and the signal voltage output from the first integrating circuit when light from the light-emitting unit illuminates the object and that outputs the first signal voltage in accordance with this difference; and (2) the second current/voltage conversion unit may include: (2a) a second integrating circuit that integrates charge in accordance with the second signal current and outputs a signal voltage corresponding to the amount of this integrated charge; and (2b) a second difference calculating circuit that finds the difference of the signal voltage output from the second integrating circuit when no light from the light-emitting unit illuminates the object and the signal voltage output from the second integrating circuit when light from the light-emitting unit illuminates the object and that outputs the second signal voltage in accordance with this difference. In this case, in the first (second) current/voltage conversion unit, charge is integrated on the first (second) integrating circuit in accordance with the first (second) signal current, with the result that a signal voltage corresponding to the amount of this integrated charge is output from the first (second) integrating circuit. The difference of the signal voltage that is output from the first (second) integrating circuit when no light from the light-emitting unit illuminates the object and the signal voltage that is output from the first (second) integrating circuit when light from the light-emitting unit illuminates the object is found by the first (second) difference calculating circuit and a first (second) signal voltage is output corresponding to this difference. The background light component is thereby canceled, so that the position of incidence of the beam that is to be detected by the semiconductor position detecting element can be accurately found.
Also, in the first or second optical position detecting the device according to present invention, (1) the first current/voltage conversion unit further includes a first mean background component cancel circuit that cancels the mean value of the contribution of background light from the first signal current that is output from the first output terminal of the semiconductor position detecting element and (2) the second current/voltage conversion unit further includes a second mean background component cancel circuit that cancels the mean value of the contribution of background light from the second signal current that is output from the second output terminal of the semiconductor position detecting element. In this case, since the mean value of the contribution of the background light is canceled by the first (second) mean background component cancel circuit from the first (second) signal current that is output from the first (second) output terminal of the semiconductor position detecting element, the beam incidence position on the semiconductor position detecting element can be even more accurately found.
A distance measurement device according to the present invention comprises: (1) a light-emitting unit that illuminates an object with a spot beam or slit beam; (2) an optical position detection device as aforesaid that detects the reflected light of the light from light-emitting unit illuminating the object; and (3) a distance calculating unit that finds the distance to the object using the position of beam incidence on the semiconductor position detecting element found by the optical position detection device. With a distance measurement device according to the present invention, a spot beam or slit beam from the light-emitting unit illuminates the object and the reflected beam therefrom is detected by the optical position detecting device. The distance to the object is then found from the position of incidence of the beam on the semiconductor position detecting element found by the optical position detecting device by the distance calculating unit.